Oranda is mainly a side-view fish, so you don't want the tail to open up horizontally flat.
Both depth and size of the tank (housing) effect how the fish turns out.
Deeper water has higher pressure, larger space to dash around also encourage the tail to close.

You can start with shallow water, so that the tail ray can get stronger and spread more during the younger stage.
As the fish gets older in the later development stage, you can increase the water height, as high as 1m! (This is practice by some commercial breeder).

To achieve head growth, feed food with heavy protein content. You can read in other thread on this.